Uniform plasma for drill smear removal reactor

ABSTRACT

A system for generating a substantially uniform plasma for processing a substrate having two major surfaces. Each of the substrate major surfaces may have electrically conductive portions. Two electrodes are oppositely disposed with respect to one another on either side of the substrate. A first r.f. power source is electrically connected to the first electrode and a second r.f. power source is electrically connected to the second electrode. The first and second r.f. power sources are out of phase with respect to one another, resulting in the generation of a substantially uniform plasma field.

RELATED APPLICATIONS

This application is related to the following concurrently filed patentapplications assigned to the present assignee: Ser. No. 692,143, for"Reactor for Plasma Desmear of High Aspect Ratio Hole" by Lo, et al andSer. No. 692,144, for "Side Source Center Sink Plasma Reactor" by Babu,et al.

BACKGROUND OF THE INVENTION

The present invention relates to a system for treating substrates byplasma and, more particularly, to a system for generating uniform plasmafor processing a substrate having two major surfaces.

In the manufacture of many electronic components, such as integratedcircuits, there is a need to deposit metallic films on substrates.Materials such as copper may be deposited on ceramic or glass substratesand then etched or otherwise fabricated into the electrical circuitsand/or components.

In the field of plasma deposition, an atom may be displaced from thesurface of a target connected to a cathode by a process calledsputtering or sputter deposition. In this process, the target is mostoften constructed of electrically conductive material such as copper orthe like. The cathode to which the target is attached is subjected to arelatively high voltage, either DC or radio frequency, in an inertatmosphere such as argon. The inert gas is ionized, forming an excitedgaseous state (plasma) from which positive ions escape to bombard theexposed surface of the target. By momentum transfer, the atoms orclusters of atoms of the target material are thereby dislodged. It isthis dislodging of the target atoms that is known as sputtering. Byrepeating this process, a number of these primarily neutral atoms movethrough the space in front of the target, in a relatively high vacuum.Eventually these atoms strike and condense on the surface of a receiver,known as a sample or substrate, which is generally in close proximity tothe target. A coating of atomic or molecular layers of target materialcan thus be built on the substrate. The coating, which is generally lessthan 1 μm, is called a thin film. It is generally sufficient for themetallization of integrated circuits.

Through holes or viaduct holes (commonly called vias) are paths forelectrical interconnections between a first-level conductive pattern anda second or higher-level conductive pattern. In order to electricallyconnect circuits on different substrate levels to each other, preciousmetal (e.g., palladium) seeding and electroless metal deposition havebeen used to coat the walls of the vias, often followed byelectroplating. Most recently, however, plasma technology has beenapplied to this problem.

In the field of plasma processing of substrates for use as printedcircuit boards and cards, nonuniformity of a plasma field can result innonuniform etching, nonuniform deposition and/or nonuniform cleaning ofvia holes and through holes, the latter being referred to as desmearing.In the etching process, for example, a more intense plasma field in thecenter of a board results in a higher etching rate for that portion ofthe board, whereas a relatively sparse plasma density at the edges ofthe board results in a proportionally and predictably low etch rate forthose sections. It has been found that nonuniformity of an electricfield in proximity to an electrically floating printed circuit boardresults in nonuniform plasma treatment thereof.

Normally, oppositely charged electrodes are provided in a vacuum chamberto initiate a plasma reaction. Such apparatus is shown, for example, incopending patent application, Ser. No. 587,098 filed Mar. 7, 1984 for"Shield for Improved Magnetron Sputter Deposition into SurfaceRecesses," and assigned to the present assignee.

For desmearing via holes and through holes, one technique is disclosedin U.S. Pat. No. 4,230,553, issued to Bartlett, et al. This techniqueuses plasma etching wherein the conductive surface layers of drilledboards are themselves the electrodes that help generate plasma. Theplasma forms directly within the holes to remove the smear. A radiofrequency (r.f.) generator is electrically connected to one surface ofeach of the boards being processed. The other surface of each of theboards is grounded. The plasma generated in this system is thus presentonly in the through holes. One r.f. source supplies power to the system.

It should be noted, however, that, while in a uniform electric fieldrelatively low radio frequencies can drive ions through the substrate'sthrough holes, this practice used in a nonuniform electric field has theopposite effect: nonuniformity of the etching process is exacerbated.

U.S. Pat. No. 4,285,800, issued to Welty, discloses a gas plasma reactorfor treatment of printed circuit boards. Included in the reactor is arack assembly having a plurality of spaced apart bars for holding thesubstrates. A pair of electrodes is positioned outside the rackassembly. The rack assembly is maintained at ground potential and theelectrodes are energized with r.f. energy to form plasma between theelectrodes and the rack bars.

The aforementioned references are not appropriate for etching largesubstrates on both major surfaces or for generating uniform plasmafields over a large area.

It would be advantageous to provide a plasma reactor system forgenerating uniform plasma fields.

It would further be advantageous to provide a plasma system foruniformly processing the major surfaces as well as the via holes andthrough holes of large substrates.

Moreover, it would be advantageous to provide a plasma reactor in whichthe substrate is maintained at a fixed voltage potential relative tor.f. power supplies.

It would also be advantageous to maintain a substrate to be plasmaprocessed at zero volts in a reactor system.

It would further be advantageous to provide a plasma reactor in whichtwo r.f. power sources are out of phase with respect to one another toattain a more uniform plasma field.

It would further be advantageous for the plasma reactor r.f. powersources to be 180° out of phase with one another.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a system forgenerating a substantially uniform plasma for processing a substratehaving two major surfaces. Each of the substrate major surfaces may haveelectrically conductive portions. Two electrodes are oppositely disposedwith respect to one another on either side of the substrate. A firstr.f. power source is electrically connected to the first electrode and asecond r.f. power source is electrically connected to the secondelectrode. The first and second r.f. power sources are out of phase withrespect to one another, resulting in the generation of a substantiallyuniform plasma field.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained byreference to the accompanying drawings, when taken in conjunction withthe detailed description thereof and in which:

FIG. 1 is a schematic representation of prior art apparatus forproducing a plasma field;

FIG. 2 is a schematic representation of prior art apparatus for creatinga plasma field surrounding a substrate;

FIG. 3 is a schematic representation of apparatus in accordance with thepresent invention for creating a uniform plasma field;

FIG. 4 is a sectional schematic representation of a reactor chamber;

FIG. 5 is a perspective view of a plurality of substrates and hollowelectrodes showing gas distribution for use therewith;

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5;

FIG. 7 is a top sectional view of a continuous apparatus in accordancewith the present invention; and

FIG. 8 is an alternative embodiment of a continuous apparatus for plasmaprocessing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a cross sectional view of aconventional upper panel electrode 10 and a lower panel electrode 12, asis well known in the prior art. Both electrodes 10 and 12 have majoraxes parallel to one another. This configuration is referred to asparallel plate panel electrodes.

A power supply, not shown, is connected to each of these electrodes 10and 12. A positive charge is applied to the upper electrode 10 and anegative charge is applied to the lower electrode 12, as shown in FIG. 1at a given instant of time. The electrical field between parallelelectrodes 10 and 12, identified by reference numeral 14, issubstantially uniform in the center region. The electrical field is moreintense at both edges of the electrodes 10 and 12, however, as shown byreference numerals 16 and 18, respectively. Accordingly, neither theelectrical field 14 nor the resulting plasma, not shown, is uniform atall locations proximate the electrodes 10 and 12.

Referring now also to FIG. 2, there is shown a cross sectional view ofthe same parallel plate panel electrodes 10 and 12 with a substrate 20therebetween. The substrate 20 has a major axis substantially parallelto the major axis of the electrodes 10 and 12. The electrical field at agiven instant of time has relatively low intensity in the center region22 proximate the electrodes 10 and 12 and relatively high intensity atthe outer edge regions 24 and 26 proximate the electrodes 10 and 12. Itcan be seen that conventional parallel plate panel electrodes 10 and 12with a substrate 20 intermediate them results in a nonuniform electricalfield.

Referring now also to FIG. 3, there is shown a plasma reactor systemhaving an upper electrode 28 and a lower electrode 30 parallel thereto.Intermediate these two electrodes 28 and 30 and substantially parallelthereto, is a substrate 32 which is grounded or maintained at zeroelectrical potential.

An r.f. source of power or generator 34, such as Model No. PM 145manufactured by the Branson IPC Co., is electrically connected to theupper electrode 28. A second r.f. source of power 36 is electricallyconnected to the lower electrode 30. In order to match impedance, animpedance matching network 38 is connected to the upper r.f. powersource 34 in series with the upper electrode 28. The impedance matchingnetwork includes fixed and variable capacitors. A second impedancematching network 40 is connected to the second r.f. power source 36 inseries with the lower electrode 30.

Alternating current phase diagrams 42 and 44 indicate the phasedifferential between r.f. power sources 34 and 36. It can be seen thatthe r.f. power sources 34 and 36 are 180° out of phase with one anotherat all times. It can also be seen that the electrical field generatedbetween the upper and lower electrodes 28 and 30, respectively, issubstantially uniform along the length of the substrate 32, includingthe end portions 46 and 48 thereof.

Referring now also to FIG. 4, there is shown a reactor chamber 50suitable for maintaining a high vacuum for use in plasma processes. Sucha chamber 50 can be obtained from the Branson IPC Co., for example, asModel No. 7415. The chamber 50 is evacuated and then argon and oxygen orCF₄ and oxygen are introduced thereto. A housing 52 is disposed withinthe reactor chamber 50. In the housing 52 are mounted a plurality ofcards or boards 54 suitable for having electrical circuits printedthereon. The boards 54 are electrically connected to one another bymeans of a bus structure 56 which, in turn, is grounded 57.

Electrodes 58 and 60 are placed alternately on either side of thesubstrates 54. Electrodes 58 are electrically connected to one anotherby means of a bus structure 62. The bus structure 62 is electricallyconnected to an r.f. power generator 64 which is adapted, in thepreferred embodiment, to operate at 13.5 MHz. It has been discoveredthat for high aspect ratio through holes (i.e., those whose ratio ofhole length to diameter is greater than 6:1), an r.f. power generatoroperating at a much lower frequency (e.g., 50 KHz) prevents creation ofpolymer species from feed gas. U.S. Pat. No. 4,425,210 issued to Fazlin,for example, discloses relatively low frequency r.f. values. Thus theionic plasma species etchants respond to the r.f. field to reach thethrough hole interior, providing uniform etch thereof. Phase diagram 65represents the phase of the r.f. generator 64 at a given moment of time.

Similarly, remaining electrodes 60 are connected to one another by meansof another bus structure 66. Bus structure 66 is electrically isolatedfrom, although physically supported by, bus structure 56 by means ofinsulating members 66a and 66b. This second bus structure 66 iselectrically connected to a second r.f. power generator 68 also adaptedto operate at 13.5 MHz. Phase diagram 69 represents the phase of secondr.f. generator 68. The electrical signal from the first r.f. generator64 is 180° out of phase with the electrical signal generated by thesecond r.f. generator 68 in the preferred embodiment. A comparison of ACphase diagrams 65 and 69 indicates this phase differential relationship.

It has also been discovered that a phase differential between the r.f.power generators 64 and 68 results in a more uniform electric field thancan be obtained either by a single r.f. power generator or by aplurality of r.f. generators, all being in phase with one another. Thephase differential need not be 180°. Thus, it should be understood thatany phase differential between r.f. power generators 64 and 68 is withinthe scope of the present invention. It should also be understood that inanother embodiment only one r.f. generator need be used in conjunctionwith the reactor chamber 50, provided that two or more electrical outputsignals are independently created thereby, each being out of phase withone another.

Gas inlet and gas outlet pipes or tubes, not shown, are connected to thereactor chamber 50 to introduce gas thereto or to remove gas therefromas required. In operation, continuous gas introduction and exhaust canbe accomplished by one or more of such lines connected to the chamber50.

Referring now also to FIG. 5, there is shown a hollow electrode plasmasystem. This hollow electrode plasma system is surrounded by a plasmachamber, not shown, the interior of which is covered and protected bynonconductive material such as Teflon material. (Teflon is a registeredtrademark of E. I. duPont de Nemours Co.).

A first hollow electrode 70 has a plurality of holes 72 drilled orpunched in one major surface thereof. The holes are shown in phantom inFIG. 5. The holes 72 are also shown in a rectilinear, uniform matrixpattern in the preferred embodiment. But it should be understood thatany pattern of holes 72 that ensures uniform gas distribution may beused.

In spaced apart relationship to this first hollow electrode 70 is asubstrate 74, the major axis of which is parallel to the major axis ofthe electrode 70. Connected to the electrode 70 is an r.f. power supply76. The substrate 74 is grounded.

Immediately adjacent and substantially parallel to the substrate 74 is asecond hollow electrode 78 having a plurality of holes, not shown,drilled or punched through both major surfaces thereof. A second r.f.power supply 80 is electrically connected to this hollow electrode 78.In a like manner, another substrate 82 is positioned substantiallyparallel to the hollow electrode 78 and is also grounded.

A third hollow electrode 84 is positioned substantially parallel to thesubstrate 82. This electrode 84 also has a plurality of holes, notshown, drilled or punched completely therethrough. Another r.f. powersupply 86 is connected to this hollow electrode 84. Another substrate 88is placed substantially parallel to the third hollow electrode 84 and isalso grounded.

Finally, a fourth hollow electrode 90 having holes, not shown, drilledor punched therethrough on one major surface only is placedsubstantially parallel to the substrate 88 and is, in turn, electricallyconnected to a last r.f. power supply 92.

Gas inlet pipes 94, 96, 98 and 100 are connected to the hollowelectrodes 70, 78, 84 and 90, respectively. Independently operablevalves 94a, 96a, 98a and 100a are placed in corresponding inlet pipes94, 96, 98 and 100 to shut off the flow of gas therethrough. Connectedto the inlet pipes 94, 96, 98, 100 is an inlet manifold 101 fordistributing gas evenly to the hollow electrodes 70, 78, 84, 90.

On the side of the electrodes opposite the gas inlet manifold 101 aregas outlet pipes, one of which being 102, having independently operablevalves 102a corresponding to each pipe. The gas outlet pipes associatedwith hollow electrodes 78, 84 and 90 are not shown in FIG. 5. All of thegas outlet pipes are connected to their associated hollow electrodes andto an outlet manifold 104 for allowing gas to be exhausted from thehollow electrodes uniformly.

A main gas feed line 106 is connected to the inlet manifold 101.Similarly, a main gas exhaust line 108 is connected to the outletmanifold 104.

It should be understood that the function of the gas inlet lines 106,94, 96, 98, 100 and manifold 101 and the function of the gas outletlines 108, 102 and manifold 104 can be reversed, if desired. That is,when appropriate, gas may be introduced by means of the main gas exhaustline 108 and exhausted by means of the main gas feed line 106.

The use of inlet and outlet pipes in direct conjunction with hollowelectrodes maximizes gas distribution and flow across the substrates,thus ensuring uniformity of gas flow as well as uniformity of electricfield. The advantage of these combined uniformities is a more accurateand uniform etching or deposition during the plasma process.

The function of valves 94a, 96a, 98a, 100a, 102a and those not shownshould also be described for a clear understanding of the hollowelectrode plasma system. When gas is introduced under pressure from themain gas feed line 106 through the inlet manifold 101, valves 94a, 96a,98a and 100a are placed in an open position to allow the gas to reachand enter the hollow electrodes 70, 78, 84 and 90 respectively. When theoutlet pipe valves 102a and others, not shown, are placed in a closedposition, the gas is forced through the hollow electrode holes 72. Inthis manner, gas introduced into the hollow electrodes 70, 78, 84, 90under pressure by means of the corresponding gas inlet ports 94, 96, 98,100 is distributed through the electrode holes 72 to impinge on thesubstrates 74, 82, 88 in a substantially uniform manner.

It can be seen that suitable settings of inlet valves 94a, 96a, 98a and100a and outlet valves 102a and others, not shown, can result in gasflowing through the hollow electrodes 70, 78, 84, 90 in any one of anumber of gas flow patterns. Individual substrates or groups ofsubstrates can be processed by appropriately setting the inlet andoutlet valves and selecting the main gas feed line 106 and main gasexhaust line 108. It should also be understood that any number of hollowelectrodes and alternating substrates may be used in accordance withthis invention.

The gas inlet lines 94, 96, 98 and 100 are used to introduce gas withwhich a plasma reaction may be maintained. Such gases are commonly CF₄,O₂, ammonia, freon and the like. A gas composition having a mixture ofany of the aforementioned molecules can also be used. Moreover, aspreviously mentioned, a mixture of argon and oxygen can be used withrelatively low r.f. power generator frequencies to clean high aspectratio through holes.

In the preferred embodiment, the phase differential among r.f. powersources is as follows. R.f. power supplies 76 and 86 are in phase withone another. R.f. power supplies 80 and 92, while being in phase withone another, are 180° out of phase with the aforementioned r.f. powersupply pair 76 and 86. Typical frequencies are in the range of 50 KHz to13.5 MHz.

Referring now also to FIG. 6, there is shown a cross-sectional portionof hollow electrodes 70 and 78 and substrate 74 therebetween, takenalong line 6--6 of FIG. 5. The hollow electrode 70 has two walls: aleft, solid wall 109 and a right wall 110 with holes 72. The holes 72 ofthe right wall 110 of electrode 70 are tapered in such a way as to allowa dispersion of gas from the left portion of the reactor chamber 50(FIG. 4) to the right portion thereof. Thus, the holes 72 in electrode70 have a smaller diameter on the left side of wall 110 and a largerdiameter on the right side of wall 110 of the electrode 70.

The orientation of the tapered holes 72 is reversed on the left wall 112of the hollow electrode 78 so as to allow uniform gas distribution tothe rightmost major surface of the substrate 74. It should be understoodthat tapering of the holes 72 in the manner shown is useful for onesubstrate 74 shown in this example placed intermediate two hollowelectrodes 70 and 78. Alternative arrangements and orientations ofelectrode holes 72 can easily be designed for modifications to theplasma process, depending on gas flow direction and number of substratesto be processed concurrently.

Referring now also to FIG. 7, there is shown a top view of a systemadapted for use in a continuous plasma treatment process having uniformgas flow and uniform electric field. A vacuum lock 114 is connected to alinear reactor chamber 115. The vacuum lock 114 is used to permitsubstrates 122a, 122b, 122c or other articles to enter the reactorchamber 115 and move along a transport track 123 without affecting theatmosphere or vacuum therein.

Within the reactor chamber 115 and on one side of the centerline thereofare three hollow electrodes 116 which are electrically connected to anr.f. power supply, RFl. These three electrodes 116 are thus inelectrical phase with one another.

Three other hollow electrodes 118 are disposed on the opposite side ofthe reactor centerline, each of which corresponding to one of theaforementioned electrodes 116. The electrodes 118 are electricallyconnected to a second r.f. power supply RF2 and are in phase with oneanother, but 180° out of phase with respect to electrodes 116.

A second vacuum lock 120 is attached to the reactor chamber 115 on theside opposite the first vacuum lock 114. Vacuum lock 120 is used toremove substrates 122a, 122b, 122c from the reactor chamber 115 withoutaffecting the atmosphere or vacuum therein.

In FIG. 7, substrates 122a, 122b, 122c are shown in a verticalorientation. It should be understood that the orientation of theelectrodes 116 and 118 may likewise be parallel to one another andhorizontally disposed, similar to the schematic orientation shown inFIG. 3. The substrates 122a, 122b, 122c are grounded in the preferredembodiment, but may be maintained at a fixed voltage potentialthroughout the plasma process.

In operation, the substrates 122a, 122b, 122c are advanced along thetransport track 123 from the initial vacuum lock 114 through the reactorchamber 115, between hollow electrodes 116 and 118 and through secondvacuum lock 120. A drive mechanism, not shown, advances each substrateon the transport track 123 linearly from one location in the reactorapparatus to another sequentially and continuously. Heating elements124, disposed within the initial vacuum lock 114, can be used to preheatthe substrates 122a, 122b, 122c before plasma etching or depositionoccurs.

Provision is made, not shown, for introducing and exhausting gas used inplasma treatment through the hollow electrodes 116 and 118 in accordancewith the description hereinabove presented in conjunction with FIG. 5.The flow of gas through the hollow electrodes 116 and 118 and around andthrough the substrates 122a, 122b, 122c is shown in FIG. 7 as arrowedlines. The hollow electrodes 116 and 118 have apertures on both sides aswell as a series of holes forming a center sink intermediate the wallsfacing the substrates 122a, 122b, 122c.

In an alternate embodiment, not shown, the reactor chamber 115 can bedivided into two or more sections, each being isolated from one anotherand each being adapted to process substrates with a different gaseouscomposition. Alternatively, one or more secondary reactor chambers canbe placed between the primary reactor chamber 115 and the vacuum lock120 in each of which a different plasma process can be maintained, eachindependently from one another. Such a series of plasma treatment stagescan be useful, for example, in etching, hole cleaning, board preparationand deposition or any combination of the above.

Referring now also to FIG. 8, there is shown a circular reactor chamberfor continuous or semi-continuous plasma processing. The unit comprisesessentially two cylindrical elements 130 and 132 at the upper and lowerends of which are secured upper and lower closure plate members, notshown in this top cross sectional view.

The inner cylinder 132, which forms the vacuum manifold 134, providesfor connecting into a central vacuum pump.

Between the outer and inner cylinders 130 and 132, numerous suitableradial partition assemblies such as 136 and 138, extending generallyradially, divide the apparatus into a number of separate processingregions or chambers, such as 140 through 154, inclusive. These separatechambers are constructed so that a ring-like platform, not shown, may besuitably rotated within and through them to carry substrates.

A conventional air lock or vacuum lock element 156 leads into one of thechambers 140 and provides for loading and unloading the substratescarried on the rotary ring platform. The control provides essentially avacuum locking device which isolates the load and unload chamber 140from all other portions of the unit. Isolation of the vacuum processingchambers 140 through 154 is achieved and effected by providing anextremely close tolerance between the substrate carrier platform and adifferentially pumped isolation compartment 141.

The carrier platform is arranged to pass from one chamber, such as 142into an adjacent chamber 144, through openings provided in the walls ofthe radially extending partition assembly members 136 and 138. Theseopenings are usually arranged in a rectangular form through the use of aseries of right angled duct-like elements 158 to provide a controlledleakage path at both the top and the sides through which the platformmoves. One side of the angled elements 158 is fastened to the partitionwall 136, while the other side is free, except for the connection at theabutting edges which are welded or soldered to make a tight fit. Thiscontrolled leakage path provides efficient isolation of one processenvironment from another.

The ring platform may be driven from any desired form of prime moversuch as a motor and appropriate gears, not shown. The outer edge of thering-like platform may be formed as a toothed member, for example, withthe teeth adapted to mesh with the teeth of a driving pinion so thatrotation is readily achieved. Of course, other forms of drives such asfrictional members may be utilized. The apparatus described here ispurely for convenience.

As can be appreciated from the showing of FIG. 8, the central vacuummanifold 134 is common to all of the formed chambers, 140 through 154.

A valve element 160 of the generally butterfly type leads from eachformed processing chamber into this central manifold 134. By suitablerotation of the valve 160, the specified processing chamber can beopened to the manifold 134 or can be closed off therefrom. In this way,a single high speed vacuum pumping system, such as a diffusion or turbopump, when connected to lead to vacuum manifold 134, can provide thenecessary vacuum to all of the different formed processing chambers andradial partition assemblies. The pumping system can be further connectedto various mechanical pumps for establishing desired vacuum level.

Each of the separate valves 160 constitutes a controllably variableconductance element which is supported in the inner cylindrical wall. Itis thus possible to have a multiplicity of differentially pumpedprocessing chambers because of the radial partition assembliesseparating each from the central vacuum manifold 134.

The vacuum manifold communication to the radial partition assembliesbetween the separate chambers, such as 144 and 148, is provided by afixed or controllable conductance entrance port 162 connected tocorresponding isolation compartments between walls such as 136 and 138,so that the pressure therein is almost as low as that within themanifold 134 leading to the vacuum pump. Because of leakages and similareffects, this isolating region or compartment is usually at a slightlyhigher pressure than that of the vacuum manifold 134. The highest systempressure is, of course, found within such chambers as 140, 142, 144,148, etc. It is these regions or compartments which constitute thevarious processing component volumes.

The ring platform successively moves within the different processingchambers and, as this occurs, the supported substrates which may beincluded within an appropriate atmosphere introduced in any appropriateand desired manner may be sputter treated by r.f. excitation ofsputtering cathode elements 164 positioned within the various chambersor other vacuum processes. If desired, and in order that the relativepressures in the different chambers shall be separably controllable, itis apparent that each of the control mechanisms conventionallyrepresented for turning the valves 160 may be automatically operated.The directly pumped controlled leakage slots in the radial partitionassembly 136, 138 eliminate process chamber contamination from onecompartment to that adjacent to it.

In operation, the substrate carrier platform is confined to the vacuumenvironment. This reduces out-gassing. The directly pumped radialpartition assemblies, as already noted, serve substantially to eliminatecompartment contamination.

A 4 ft. diameter circular processing chamber is approximately theequivalent of an 11 ft. length linear, in-line section. The circularprocessing system provides for substrate loading and unloading inadjacent areas, as contrasted with the in-line system which requiresloading and unloading at opposite ends of the system, as previouslydescribed.

In addition, the circular arrangement (FIG. 8) with the centrallylocated pumping system beneath the processing chambers makes necessaryonly a single pumpout unit.

With the circular reactor arrangement, the loading of substrates as wellas the unloading thereof is achievable by any desired form of simpleautomatic method and permits a continuous or semi-continuous operationwithout causing the environment to vary. It is also readily controllableby computer control for different types of processing and purelyautomatic operation.

It should be understood that the circular reactor apparatus, as well asthe longitudinal reactor apparatus described in FIG. 7, can be used withboards or substrates transported either vertically or horizontally.

An oxygen plasma can be used in the continuous plasma device hereinabovedescribed to improve adhesion between copper, the most commonly usedelectrical,conductor, and epoxy, a nonconductive material.

Since other modification and changes varied to fit particular operatingrequirements and environments will be apparent to those skilled in theart, the invention is not considered limited to the examples chosen forpurposes of disclosure, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

What is claimed is:
 1. An apparatus for generating a substantiallyuniform plasma for processing a substrate having two major surfaces,each of said major surfaces having electrically conductive portionsdisposed thereon, comprising:(a) two electrode means oppositely disposedwith respect to one another on either side of said substrate; (b) afirst radio frequency power source operatively connected to the first ofsaid electrode means; and (c) a second radio frequency power sourceoperatively connected to the second of said electrode means, said secondradio frequency power source being out of phase with respect to saidfirst radio frequency power source.
 2. The apparatus in accordance withclaim 1 wherein said first and second radio frequency power sources are180 degrees out of phase with respect to one another.
 3. The apparatusin accordance with claim 1 wherein said substrateis maintained at afixed voltage potential.
 4. The apparatus in accordance with claim 3wherein said fixed voltage potential is zero volts.
 5. The apparatus inacordance with claim 3 wherein said fixed voltage potential is less thanzero volts.
 6. The apparatus in acordance with claim 1 wherein saidelectrically conducive portions of said substrate are electrical lines.7. The apparatus in accordance with claim 2 wherein said substrate ismaintained at a fixed voltage potential.
 8. The apparatus accordancewith claim 7 wherein, during said plasma processing, material isdeposited onto said substrate.
 9. The apparatus in accodance with claim7 wherein, during said plasma processing, material is etched from saidsubstrate.
 10. The apparatus in accordance with claim 7 wherein, duringsaid plasma processing, material on said substrate is oxidized.
 11. Theapparatus in accordance with claim 7 wherein, during said plasmaprocessing, material disposed on said substrate is reduced.
 12. Theapparatus in accordance with claim 7 wherein said plasma is used toclean material disposed on said substrate.
 13. The apparatus inacordance with claim 7 wherein said substrate is a printed circuitboard.
 14. The apparatus in accordance with claim 7 wherein saidsubstrate is a printed circuit card.
 15. The apparatus in acordance withclaim 7 wherein said substrate is a component of a printed circuitboard.
 16. The apparatus in accordance with claim 7 wherein saidelectode means are substantially parallel to one another.
 17. Anapparatus for generating a substantially uniform plasma for processing aprinted circuit board having thru holes therein, comprising:(a) twoelectrode means oppositely disposed with respect to one another oneither side of said printed circuit board; (b) a first radio frequencypower generator operatively connected to the first of said electrodemeans; and (c) a second radio frequency power generator operativelyconnected to said second electrode means, said second radio frequencypower generator being out of phase with respect to said first radiofrequency power generator.
 18. The apparatus in accordance with claim 17wherein said first and second radio frequency power generators are 180degrees out of phase with respect to one another.
 19. The apparatus inaccordance with claim 18 wherein said printed circuit board ismaintained at a fixed voltage potential.
 20. The apparatus in accordancewith claim 19 wherein said fixed voltage potential is zero volts. 21.The apparaus in accordance with claim 19 wherein, during said plasmaprocessing, material residing in said thru holes is etched.
 22. Theapparatus in accordance with claim 19 wherein, during said plasmaprocessing, material residing in said thru holes and proximate theretois cleaned.
 23. The apparatus in accordance with claim 19 wherein saidelectrode means are substantially parallel to one another.
 24. Apparatusfor processing a substrate having electrically conductive portionsthereon in a plasma field, comprising:(a) means for maintaining saidelectrically conductive portions at a predetermined voltage potential,said potential being invariant over the time of processing; (b) a firstelectrode means and a second electrode means in electrically operativerelationship with said substrate; and (c) a first source of radiofrequency power operatively connected to said first electrode means anda second source of radio frequency power operatively connected to saidsecond electrode means, said first and second sources of radio frequencypower having a phase differential with respect to one another.
 25. Theapparatus in accordance with claim 24 wherein said phase differential is180° degrees.
 26. The apparatus in accordance with claim 24 wherein saidpredetermined voltage potential of said electrically conductive portionsof said substrate is zero volts.
 27. The apparatus in accordance withclaim 24 wherein said predetermined voltage potential of saidelectrically conductive portions of said substrate is less than zerovolts.
 28. The system in accordance with claim 25 wherein saidelectrically conductive portions of said substrate are electrical lines.29. The apparatus in accordance with claim 25 wherein said electrodemeans are substantially parallel to one another.
 30. Apparatus forprocessing a printed circuit board having a plurality of thru holestherein in a plasma field, comprising:(a) means for maintaining saidprinted circuit board at zero voltage potential invariant over the timeof processing; (b) a first electrode means in operative relationshipwith a first portion of said printed circuit board; (c) a secondelectrode means in operative relationship with a second portion of saidsubstrate, said second electrode means being substantially parallel tosaid first electrode means; (d) a first means for creating radiofrequency power operatively connected to said first electrode means; and(e) a second means for creating radio frequency power operativelyconnected to said second electrode means, the respective frequenciescreated by said first and second means for creating radio frequencypower having a phase differential of 180 degrees with respect to oneanother.
 31. The apparatus in accordance with claim 24 wherein saidsubstrate comprises a portion of a semiconductor device.